The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A continuous variable transmission (CVT) using a belt as a variator, which is a shift mechanism, is configured to receive power transferred from an engine by a primary pulley, transfer the power to a secondary pulley through the belt, and output power shifted through the secondary pulley to driving wheels.
In the continuous variable transmission as described above, a gear ratio is continuously changed by a difference in a dynamic radius formed between the belt and the pulleys. Therefore, an oil pressure applied to a pulley piston of a driving pulley of each pulley is controlled to change a dynamic radius formed between the belt and the pulleys, thereby obtaining a desired gear ratio.
In order to smoothly transfer the power between the pulleys and the belt without being slid, pulley clamping force corresponding to force of the pulleys pushing the belt should be appropriately formed. The pulley clamping force is determined depending on an input torque input from the engine to the pulleys, and in order to form the pulley clamping force determined as described above, a target oil pressure should be determined based on the pulley clamping force to control an oil pressure applied to the pulleys by the target oil pressure.
When the continuous variable transmission is in a tip-in situation, a down shift is performed by supplying oil to a driven pulley. We have discovered that when a speed of the down shift exceeds an allowable limit value, a surplus amount of oil in channels is decreased. As a result, a phenomenon that it is impossible to follow a target line pressure occurs. In addition, when the surplus amount of oil is decreased, a damper pressure is decreased, and a damper that is held is released.
The contents described above have been provided only for assisting in the understanding for the background of the present disclosure and should not be considered as corresponding to the related art known to those skilled in the art.